1. Field of the Invention
The present invention relates to an active material used for electrochemical devices and others, and a method for producing the active material.
2. Related Background Art
A number of studies have been conducted on metal-containing particles with charge and discharge capacities larger than those of graphite (e.g., metal particles, metal oxide particles, metal sulfide particles, etc.), as anode active materials for the electrochemical devices such as lithium secondary batteries (e.g., Japanese Patent Application Laid-open Nos. 11-54155, 2001-332254, 2001-23616, 2002-270170, and 2004-311428). However, the active materials consisting of the metal-containing particles demonstrate the cycle performance considerably poorer than that of graphite. The cause of this poorer cycle performance is thought to be failure in electric conduction caused as follows: the metal-containing particles expand and constrict to become more finely powdered and the metal-containing particles become released from a current collector to result in failure in electric conduction. With the metal-containing particles, lithium ions often diffuse slow in a solid and it is often the case that the rate performance is insufficient.
The studies are thus directed toward micronization of the metal-containing particles for these reasons. The techniques for implementing the micronization include pulverization with a planetary ball mill, production of nanoparticles by CVD, production of nanoparticles by spray pyrolysis, wet reduction (Japanese Patent Application Laid-open Nos. 11-54155 and 2001-332254), dry reduction (Japanese Patent Application Laid-open No. 2002-270170), spray atomization (Japanese Patent Application Laid-open No. 2004-311428), and so on. There are also attempts to make the metal-containing particles supported in a carbon carrier (Japanese Patent Application Laid-open No. 2001-23616).